Long-term bedload mobility in gravel-bed rivers using iron slag as a tracer

Abstract

Bedload dispersion is evaluated in gravel-bed rivers using slag elements from ironworks established along rivers in the Ardenne region, between the fourteenth and the nineteenth centuries. Large quantities of slag were dumped close to these rivers or even directly into the channels. For centuries, slag elements were dispersed in the bedload and transported by floods of varying importance. Consequently, slag may be considered as a reliable tracer to analyze bedload dispersion over several centuries. The size of slag elements was studied along 16 Ardenne rivers. The longitudinal size trend of the largest slag particles allows the effective competence of these rivers to be determined (between 19 and 129 mm for rivers where specific stream power for the bankfull discharge ranges between 20 and 134 W/m²). A direct relationship doesn't exist between these two parameters as the size of slag elements must be considered with regard to the D 50 of the bed. Selective transport was analyzed directly downstream of the input sites. The sorting distance varies from river to river and depends on the velocity of the coarse elements introduced into the river since the inception of the iron industry. Downstream of two metallurgic sites, the slag propagation fronts were located. As the periods of activity at these sites are known from historical studies, the virtual velocity of bedload movement in these rivers was estimated to be 2-4 km/century.

Comparison of methods for quantifying active layer dynamics and bedload discharge in armoured gravel‐bed rivers

“…We estimated the depth of the reworked subsurface layer over a much longer period using slag residues from the metalworking industry, which were dumped into the rivers of the Ardenne region from the end of the fourteenth century (Gillard, ; Leboutte, ). Slag elements, which are similar in size to pebbles, have already been used to evaluate bedload dispersion over periods of many centuries (Sluse and Petit, ; Houbrechts et al ., ). Microscopic slag particles, which are transported in suspension, have also been used on floodplains to define the extent of aggradation and sedimentation since the Middle Ages (Henrottay, ; Houbrechts, ; Houbrechts and Petit, ) and to understand lateral mobility in rivers (Snijders et al ., ).…”

Evaluation of long-term bedload virtual velocity in gravel-bed rivers (Ardenne, Belgium)

“…For centuries, huge quantities of slag elements were dispersed in the bedload and transported by floods of varying magnitudes. Consequently, slag may be considered as a reliable tracer to analyse bedload dispersion over several centuries (Sluse and Petit, 1998;Houbrechts et al, 2011).…”

“…Lastly, slag particles from the ancient iron industry have been used to estimate the bedload velocity in some gravel-bed rivers of the Ardenne Massif. In two of these rivers, velocity has been estimated at between 2 and 4 km/century (Sluse and Petit, 1998;Houbrechts et al, 2011).…”

Dynamics and mechanics of bed-load tracer particles

“…The application of passive tracer particles has taken various forms, such as exotic lithologies (Houbrechts et al, 2011), painted bed material (Wilcock, 1997b), magnetic (Hassan et al, 1991), radioactive (Sayre and Hubbell, 1965;Bradley et al, 2010), and RFID (Lamarre et al, 2005;Bradley and Tucker, 2012;Phillips et al, 2013;Schneider et al, 2014). A benefit of RFID-equipped tracer particles is that each particle is uniquely identified, which allows its position to be measured at longer timescales with high recovery rates (Bradley and Tucker, 2012;Phillips et al, 2013).…”